Rotating element displays (REDs) are a class of electro-optic displays that use rotation of optically and electrically anisotropic elements, such as spheres, in response to an electric stimulus, for producing images. REDs include widely known gyricon electronic paper displays, which were first developed in 1970s at Xerox's Palo Alto Research Center. Further development of REDs, however, was hampered at least in part due to challenges associated with fabrication of uniform populations of optically anisotropic pixel elements.
Typically, gyricon displays employ bichromal spheres composed of wax or plastic hemispheres having dissimilar colors and charges. In one illustrative example, each bichromal sphere may have a negatively charged black hemisphere and a positively charged white hemisphere. Within the display, each sphere is suspended in a dielectric fluid contained within a cavity formed in a plasticized elastomer. Each sphere is free to rotate in the fluid so that it could turn with black or white side to the viewer, thus providing a pixel with a black or white appearance. When an appropriate voltage is applied to the electrodes addressing selected spheres, the spheres rotate in accordance with their dipole moment and display the image to the viewer.
While rotating element displays may have a variety of configurations, and may employ rotatable elements other than spheres (e.g., cylinders), they all typically require optically and electrically anisotropic elements with small dimensions. For example, electrically anisotropic black-and-white spheres with an average diameter from about 5 to 200 microns have been used in certain RED applications.
Manufacturing of such elements, however, presents many difficulties associated with specific requirements that are imposed on these elements by their intended function. These requirements include controllable distribution of charge and color on the element surface, homogeneity of element populations, size requirements, etc. Problems associated with fabrication of such elements hinder the development of RED technology and RED-based electronic paper products. Therefore, there is a continuous need for fabrication methods of optically and electrically anisotropic elements tailored for RED applications.